Over the years a large number and variety of important polymers have been developed with styrene monomers. Amorphous homopolymers of styrene prepared via free-radical polymerization are still the most important polymers. Subsequently other forms of polystyrene have been prepared. These include Ziegler-Natta isotactic crystalline polystyrene and anionic polystyrene with an M.sub.w /M.sub.n in the range of 1.05-1.10 with controlled molecular weight. Alkylated styrenes, such as alphamethyl styrene and paramethylstyrene have also been of interest for certain end uses. See, e.g., "Styrene Plastics", Kirk-Othmer Encyclopedia of Chemical Technology, Volume 19, pages 85-134 (Interscience Publishers, 1969).
It has long been known that the brittle nature of polystyrene can be overcome by incorporating a minor amount of rubber. The rubber is largely incompatible with the polymeric vinyl compounds resulting in a two-phase system comprising a dispersed rubber phase and a poly(monovinyl aromatic) matrix. See, e.g. U.S. Pat. No. 4,309,515. These graft copolymers are commonly termed high impact polystyrene or HIPS.
Acrylonitrile copolymers with styrene (SAN) are another large group of styrene polymers. These copolymers are transparent, and, in comparison to polystyrene, more solvent- and craze-resistant and relatively tough. They also constitute the rigid matrix phase of the ABS (acrylonitrile-butadiene-styrene) copolymers which are of common usage.
Styrene has long been copolymerized with butadiene to form both rubbers (SBR) and toughened plastics.
Other copolymers with styrene include .alpha.-methylstyrene copolymers, p-methylstyrene copolymer (see e.g. U.S. Pat. No. 4,230,836), methyl methacrylate copolymer, maleic anhydride copolymer and many more.
What has now been found is a new comonomer that can be copolymerized with styrene in the above-type of polymers, resulting in a new set of polymers having improved properties.